Polyamides, in particular nylon-6, and nylon-6,6, are industrially significant polymers. They are usually prepared by reacting suitable monomers such as caprolactam, adipic acid, or hexamethylenediamine, in the presence of water.
Unless further measures are taken, this gives polyamides which during downstream steps of processing, such as injection molding, have a tendency to undergo uncontrolled molecular weight increase with a resultant impairment of processing properties. In particular, an increase in melt viscosity occurs (determined as a fall-off in the melt volume flow rate to EN ISO 1133), and in injection molding, for example, this leads to longer cycle time.
To stabilize the polyamide with respect to this type of uncontrolled molecular weight increase, it is usual to use chain regulators during the preparation of the polymer, an example being propionic acid.
These chain regulators can substantially suppress the molecular weight increase but in order to shorten cycle times in injection molding it is desirable to increase the melt volume flow rate of polyamides to EN ISO 1133 while the relative viscosity determined to DIN 51562-1 to -4, remains the same.
It is an object of the present invention to provide a process which, in a technically simple and cost-effective manner, permits the preparation of a polyamide which when compared with polyamides chain-regulated by conventional methods has higher melt volume flow rate to EN ISO 1133 while the relative viscosity determined to DIN 51562-1 to -4, remains the same.